The proposed research concerns 7 problem areas ranging from psychophysical experiments on intersensory magnitude summation to sound transmission in the outer, middle, and inner ear. All the lines of planned research result directly from work performed during the preceding years of the project. Their broad overall aim is to increase our knowledge of coding and utilization of sensory information. Emphasis is on the auditory system. The 7 problem areas are entitled: 1) Nature of psychological (subjective) magnitudes and their additivity. 2) Temporal auditory integration as manifested at the threshold of audibility, in the stapedius-muscle reflex and loudness enhancement. 3) Partial linearity and nonlinearities of the auditory system, as reflected in central masking. 4) Intensity characteristics of sensory receptors: a generalized mathematical formulation. 5) Responses of auditory-nerve fibers to signals accompanied by interfering sounds. 6) The problem of interaction between cochlear inner and outer hair cells. 7) Sound transmission in the ear. The first and, partially, the second problem areas result from the discovery on the project that the magnitude of loudness has two perceptual aspects that have fundamentally different intensity, frequency and time characteristics. The aspect considered under 1) does not appear to have any sensory quality and may be common to all senses. The aspect investigated under 2) appears to bear numerical similarities to the characteristics of the threshold of audibility and the stapedius reflex. Area 3) deals with the discovery that central masking characteristics resemble single-unit characteristics of the auditory nerve, and area 4) with the discovery that all sensory receptors may have functionally similar intensity characteristics. Area 5) concerns, among other things, the discovery that short-term temporal adaptation of firing rates in auditory-nerve units results from an additive process rather than from gain control, and area 6) the growing evidence that cochlear inner and outer hair cells interact, with the outer hair cells having an inhibitory effect. Area 7) constitutes an extension of past experimental and modelling work on auditory sound transmission.